The invention relates to an alkali aluminosilicate glass. More particularly, the invention relates to a high strength, down-drawn alkali aluminosilicate glass. Even more particularly, the invention relates to a high strength, down-drawn alkali aluminosilicate glass for use as a cover plate in mobile electronic devices.
Mobile electronic devices, such as personal data assistants, mobile or cellular telephones, watches, laptop computers and notebooks, and the like, often incorporate a cover plate. At least a portion of the cover plate is transparent, so as to allow the user to view a display. For some applications, the cover plate is sensitive to the user's touch. Due to frequent contact, such cover plates must have high strength and be scratch resistant.
The touch sensitive screens of the latest such devices are typically chemically-strengthened, ion-exchangeable “soda-lime” type glasses. These are frequently complicated compositions consisting not only of Na2O (soda), CaO (lime) and SiO2 (silica), but also include several other oxides such as MgO, Li2O, K2O, ZnO, and ZrO2. These glasses are compatible with large-scale sheet glass manufacturing via floatation on a tin metal bath, but cannot be formed by methods, particularly down-draw processes such as fusion draw and slot draw processes, that are more traditionally associated with precision sheet glass. This is because liquidus temperatures of such soda lime glasses are too high—and their viscosities at the liquidus temperature too low to be compatible with fusion or slot draw processing.